For some time now, investigators have argued that there is a general slowing of cognitive processes with advancing age. In fact, the evidence has seemed overwhelmingly to favor such an account. However, recently several investigators have argued that slowing varies across domains. Other investigators have argued that slowing varies from one task or process to the next. Thus, the model of general slowing has slowly been losing ground to the other less general models. Unfortunately, all tests to date of the various models of slowing have largely ignored the content, configuration and capacity of the network of cognitive processes which governs the performance of older and younger adults. This is unfortunate because as a number of investigators have recently argued, a critical test of the various models of slowing requires a detailed knowledge of this microstructure. Theoretically, the objective of the proposed research is to develop and then undertake the necessary critical tests of the models of general, domain-specific, task-specific and process-specific slowing. The tests rely on recent developments in response time modeling which make it possible both to identify the structure of complex cognitive networks and to estimate the durations of processes embedded in such networks. The tests will be based on laboratory tasks. Practically, the objective is to determine whether the laboratory findings generalize to the field, and in particular, whether the laboratory findings can explain differences between younger and older adults' driving skills. The tests will be based on driving tasks performed in either a fully instrumented or simulated vehicle. The same model of aging should predict slowing in these driving tasks that predicts slowing in the laboratory tasks if indeed the results from the laboratory generalize to the field. In summary, the proposed research is an attempt to use what is known about the mathematics of the microstructure of cognition to explore the age related slowing of processes in both a laboratory and applied setting. This approach can potentially yield insights into the locus of aging effects which other current methods are too gross to capture.